1. Technical Field of the Invention
The present invention relates to a control apparatus for a vehicle automatic transmission, and particularly, relates to a control apparatus for a vehicle automatic transmission, which performs an automatic downshift for speed gears according to needs at the time of implementing a manual shift mode of performing a shift operation instructed by a manual operation of a driver.
2. Description of the Related Art
As a control apparatus for a vehicle automatic transmission, an apparatus is general, which prepares in advance plural type of shift maps for obtaining shift characteristics, obtains a value indicating a running resistance through acceleration, determines whether or not a vehicle is present on a flat road, an uphill road or a downhill road, selects any of the shift maps, and controls a gear ratio based on the selected shift map. That is to say, the control apparatus compares expected acceleration to be preset based on an engine output and actual acceleration to be actually obtained with each other, determines an uphill/downhill degree (road gradient), selects an optimum shift map, and decides the gear ratio based on the selected shift map.
As the control device as described above, in Japanese Patent No. 2959938 (Patent Literature 1), a control device for a vehicle automatic transmission is disclosed, in which a forcible downshift when the vehicle runs on the downhill road is made less likely to occur as the road gradient is becoming steeper as long as a deceleration intention of a driver is not strong, and enhancement of drivability is achieved.
Moreover, in Japanese Patent No. 2862538 (Patent Literature 2), a control device for a vehicle automatic transmission is disclosed, in which, when it is detected that a running road is a road (downhill road) with a predetermined down gradient or more, a brake actuation is detected, and predetermined vehicle deceleration or more is detected, then a shift line at the time of a low load is changed to shift characteristics set on a higher vehicle speed side in comparison with usual shift characteristics, whereby a violent shift caused by an accelerator operation is prevented.
As described above, the early downshift at the time of the conventional vehicle deceleration has been implemented on the downhill road, and a necessary engine brake has been ensured by the downshift concerned. Moreover, also on places other than the downhill road, the early downshift has been implemented in response to the vehicle deceleration; however, the downshift concerned has been implemented only at the time of sudden deceleration of the vehicle. Furthermore, it has been determined that an opening degree of an accelerator pedal and the vehicle acceleration are predetermined values or more, and an upshift after the downshift has been implemented based on such a determination concerned.
However, if the downshift on the places other than the downhill road is implemented only at the time of the sudden deceleration of the vehicle as described above, then it is apprehended that, at timing when the downshift and a shift hold after the downshift should be originally performed in such an event where the vehicle runs on a continuously meandering road (winding road), appropriate downshift and shift hold may not be performed, and good drivability may not be able to be ensured.
Moreover, if the determination of the downshift and the subsequent shift hold is made based on a variation of the opening degree of the accelerator pedal, then it is apprehended that, in a drive of a driver whose operation of the accelerator pedal is violent (rough), the downshift and the shift hold may be implemented at timing when the downshift and the shift hold are unnecessary. Moreover, in a drive of a driver highly skilled in driving, whose operation of the accelerator pedal is gentle, it is apprehended that the downshift and the subsequent shift hold may not be implemented at timing when the downshift and the shift hold are originally necessary. That is to say, there is a disadvantage that the timing of the downshift and the shift hold is undesirably decided only by an operation manner of the driver irrespective of a running environment such as type of a road surface on which the vehicle runs.
Moreover, as the control apparatus for a vehicle automatic transmission, which is as described above, there is an apparatus capable of implementing a normal running mode and a sport running mode in a switching manner. Here, the normal running mode is a running mode of performing shift control that is based on a normal shift map mainly for a driver who has a general skill, and the sport running mode is a running mode of performing shift control that is based on a shift mode for sport running, which has setting that makes much of running performance (running feeling, acceleration feeling and the like) in order to satisfy tastes of a driver who has a high skill. Then, in this type of the control apparatus, it is necessary to perform the downshift early (on a high vehicle-speed side) at the time of deceleration in order to ensure responsiveness at the time of re-acceleration in the sport running mode. Meanwhile, if the downshift is implemented early in the normal running mode, then an increase of the number of engine revolutions is brought about, and it is apprehended that the increase concerned may result in feeling of wrongness about drivability, such as worsening of vibrations/noise of the vehicle, and an increase of the engine brake.